This study focuses on three well defined, irradiated populations: the first, persons whose thymus glands were irradiated in infancy; the second, women whose breasts were treated with x-rays for acute post-partum mastitis; and the third, persons given x-ray treatments to the head during childhood. Longitudinal studies of reported morbidity and mortality in these populations and their controls have been ongoing for over 15 years. The effects of irradiation earlier in life on subsequent health remin evident. The objectives of the study are: (1) to elucidate the nature of radiation-induced neoplastic processes and conditions with abnormal immunological features, (2) to quantify the cancer risks of these irradiated populations, (3) to evaluate the suggested increased incidence of schizophrenia in the thymus-irradiated population, and (4) to inform our patients of a program of appropriate medical follow-up. A mailed questionnaire will be used to obtain health information. Reports of neoplasms, surgery, other serious illness and deaths will be verified. Surgically removed tissue will be examined histologically. Laboratory studies to evaluate immune status will be conducted in selected individuals.